Many electrical loads ranging from laptop to high power motor drives are powered by power electronic converters using power switching devices such as Insulated Gate Bipolar Junction Transistors (IGBT) or Metal Oxide Substrate Field Effect Transistors (MOSFET). There is an increasing requirement to improve the reliability and availability of such electrical systems, in particular by the prevention of power switching device failures.
Two common causes of power switching device failure are electrical faults and thermal stresses. Electrical faults are typically caused by exposure of the switching device to over-voltage, over-current, high rate of change of voltage or high rate of change of current conditions. Enhanced design of the gate drive circuits using de-saturation protection is generally employed to detect electrical stresses, with the gate drive circuit being arranged to rapidly reduce the gate-voltage for safe shutdown of the switching device.
Thermal stresses are generally caused by the exposure of the switching device to high currents over extended periods, high current transient spikes and long exposure to thermal cycling. Many known gate drive circuits do not consider the temperature of the switching device or its case as part of the control strategy.
Traditionally, the function of the gate driver is to apply the correct switching signals to the switching device (for example, IGBT, MOSFET devices etc.). It also provides protective features such as the ability to shut down upon detection of excessive current, voltages or device failures. Today, there are some active gate control driver topologies available in the market but their focus is limited to safe shutdown and slope control of a switching signal to reduce the electrical stress.
A known problem with existing gate drive circuits is that a single point failure or the failure of single switching device will result in the complete shutdown of the system. This is a concern in safely critical applications where system shutdown may be unacceptable. In such applications redundant systems may be employed to meet the reliability requirements. However, this generally results in a complex and expensive architecture, which requires additional hardware and control, impacting system power density.
Device over sizing may offer increased margins for the maximum current handling but will result in the design of an over sized heat sink and cooling system. Although such a solution is able to dissipate the generated heat, the system cost and weight will increase.